Non-institutionalized elderly individuals make up over 95% of our population over 65 years. Their health needs are a major concern. There is very little data about infectious diseases, including the epidemiology, impact on morbidity and mortality and the relative importance compared to other illnesses, in this non-institutionalized group. Our proposal aims to address this problem through carefully designed epidemiologic studies on a well-defined non-nursing home population greater than 65 years, conducted over a five year study epriod. Two established neighborhood health centers ataffed by our hospitals in complete control of all health care for its patients, and with excellent rapport with the community offer an ideal setting for the study. We plan to study about 1/4 of the population greater than 65. 500 elderly now attending either of the two clinics will comprise the study group, and 300 elderly from the same neighborhood who do not use the clinics will be followed to validate the study group. Prior to initiating the study period all 800 persons will be enrolled and baseline data collected. Over the study period active, intense surveillance for all clinical infectious episodes whether at home, clinic or hospital will be conducted. This will determine types of infection and their outcome, their impact on mobility and mental function, patterns of transmission, and relative importance compared to other non-infectious illnesses. A sophisticated data storage and retrieval system will both facilitate surveillance and permit ongoing analysis by the team of physicians, nurses, epidemiologists, infectious disease specialists, and statisticians involved. The information derived from these studies should provide the necessary foundation for design and long term execution of appropriate intervention studies in the same setting and groups. In summary, our fundamental hypothesis is that clinical infections contribute substantially to morbidity and possibly to mortality in an ambulatory elderly population, and that it will be possible ultimately to reduce this morbidity by careful surveillance, follow-up and treatment.